The subject matter described herein relates to surface inspection techniques, and more particularly to semiconductor device pattern generation.
Photolithography (also referred to as lithography) is commonly used during formation of integrated circuits on semiconductor wafers. In the context of design and manufacture of semiconductor devices, the terms lithography or photolithography refer to the process of patterning openings in photosensitive materials (sometimes referred to as photoresists or resists) which define small areas in which a silicon base material is modified by a specific operation in a sequence of processing steps.
A basic photolithography system includes a radiation source, a stencil or photo mask containing the pattern to be transferred to a wafer, one or more lenses, and a means for aligning existing patterns on the wafer with patterns on the mask. A form of radiant energy such as, for example, ultraviolet light may be passed through a radiation patterning tool and onto a radiation-sensitive material (such as, for example, photoresist) associated with a semiconductor wafer. The radiation patterning tool may be referred to as a photomask or a reticle.
The term photomask traditionally is understood to refer to masks which define a pattern for an entirety of a wafer, and the term reticle is traditionally understood to refer to a patterning tool which defines a pattern for only a portion of a wafer. However, the terms photomask (or more generally mask) and reticle are frequently used interchangeably in modern parlance, so that either term can refer to a radiation patterning tool that encompasses either a portion or an entirety of a wafer. For purposes of interpreting this disclosure and the claims that follow, the term reticle is utilized generically to refer to any radiation patterning tool, inclusive of tools which define a pattern for only a portion of a wafer and tools which define a pattern for an entirety of a wafer.
Reticles contain light restrictive regions (for example, totally opaque or attenuated/half-toned regions) and light transmissive regions (for example, totally transparent regions) formed in a desired pattern. A grating pattern, for example, can be used to define parallel-spaced conductive lines on a semiconductor wafer. As discussed previously, the wafer is provided with a layer of radiation-sensitive material such as, for example, photoresist.
As described above, radiation from the radiation source passes through the reticle onto the layer of photoresist and transfers a pattern defined by the radiation patterning tool onto the photoresist. The photoresist is then developed to remove either the exposed portions of photoresist for a positive photoresist or the unexposed portions of the photoresist for a negative photoresist. The remaining patterned photoresist can then be used as a mask on the wafer during a subsequent semiconductor fabrication step, such as, for example, ion implantation or etching relative to materials in the wafer proximate the photoresist.
Various forms of interference such as, e.g., diffraction effects, can cause the geometry created in the photoresist to deviate from the geometry the reticle was intended create on the photoresist. The deviation becomes increasingly problematic as semiconductor design uses increasingly smaller line widths.